Four-wheel drive vehicles are popular for use off road and for providing improved traction on snowy, icy, and other slippery roads. Four-wheel drive vehicles are often provided with the capability of disconnecting the secondary driving axle in order to provide a two-wheel drive mode when using four-wheel drive mode is not beneficial. However, even in the two-wheel drive mode, many of the drive components are driven by rotation of the wheels which are in engagement with the road. Accordingly, wheel end disconnects and center disconnects have been developed in order to disconnect either the wheels or the axles from the remaining driveline system so that all of the components of the driveline are not rotated by rotation of the non-driven wheels of a four-wheel drive vehicle. It has been found that disconnection of the driveline components from the non-driven wheels can significantly reduce the amount of torque demand for driving the vehicle as well as increasing the fuel efficiency of the vehicle when operated in the two-wheel drive mode. Although suitable disconnect mechanisms have been developed for use with four-wheel drive vehicles, it is still desirable to provide a more reliable and less expensive driveline disconnect system.
Conventional driveline disconnects utilize actuators that include a threaded lead screw which is engaged by a nut follower for providing connection of the driveline disconnect. When these conventional systems are shifted into the four-wheel drive (connect) position, the force exerted by the axle return spring and/or actuator block shift spring to the actuator nut follower is transmitted back to the actuator gear train. These forces, along with vehicle vibration over long periods of time, can potentially backdrive/creep the nut follower so as to negatively impact the operation of the conventional actuator device. In addition, conventional actuators require the use of a bi-directional motor for moving the driveline disconnect between the connected and disconnected positions. The bi-directional motion in these conventional actuators applies excessive stress on the motor, shafts, gears, and supporting joints, especially during a rapid shift cycle. Hence, these excessive stresses deteriorate the actuator's life and performance. Additional components and electrical circuitry are required that contribute to added cost and complexity. The travel of a nut follower, in conventional actuators, is also constrained by a mechanical stop. This mechanical stop creates a potential for the actuator to be jammed. Furthermore, in the conventional actuator, the motor needs to develop a high torque level at the beginning of a shift that applies undesirable stresses on the motor and other actuator components.
The disconnect actuator of the present invention provides the force and stroke required by a coupling member to engage and disengage a coupler for providing connection between a first and second rotatable member. A one-way electric motor is utilized and is operable to drive a gear mechanism and associated cam mechanism. A cam follower is engaged with the cam mechanism and is supported for linear motion relative to the cam mechanism and is engageable with the coupler device for moving the coupler to one of an engaged and disengaged position. The cam mechanism and cam follower are arranged such that rotation of the cam mechanism in 180 degree increments provides connection and subsequent disconnection of the coupler device while utilizing the one-way motor. The driveline disconnect actuator of the present invention utilizes a relay switch (for example, a single pole double-throw) with a stationary encoder and a rotating wiper that provides a relatively simple low cost switching circuit as compared to the costly electronic circuitry typically required for conventional actuators using bi-directional motor control.
Furthermore, the system of the present invention is immune to the backdrive phenomenon associated with conventional actuators in that the rotation of the worm/cam from 0 to 180 degrees transfers into linear displacement of the cam follower to cause a shift from a two-wheel drive operating mode to a four-wheel drive operating mode. The rotation of the worm gear from 180 degrees to 360 degrees transfers into linear displacement of the cam follower to cause a shift from the four-wheel drive mode to a two-wheel drive mode. Therefore, either at the 0 or the 180 degree position of the cam, the exerted forces are transmitted to the worm gear, supporting pin, and the housing and do not contribute to a backdrive phenomenon as experienced with conventional actuators.
The use of a one-way motor also improves the disconnect actuator's performance and reduces the cost. Because the motor and gear train rotate in one direction only, it reduces the stress on the motor, shaft, gears, and supporting joints. The bi-directional motion in conventional actuators applies excessive stress on the motor, shafts, gears, and supporting joints.
The driveline disconnect actuator of the present invention also eliminates the problem of jamming, since the use of a 180 degree rotating cam mechanism does not utilize a mechanical stop, there is no potential for jamming. Finally, since the actuator linear displacement of the present invention is the sine function of a one gear angular rotation, and since the motor's peak torque is at 90 degree rotation of the worm gear, the motor starts up with ease since at start-up, minimum torque is required. At the start of any shift, the present invention allows the motor to accelerate to high speed before approaching a peak torque. However, in conventional actuators, the motor needs to develop a higher torque immediately at a beginning of a shift. Furthermore, the worm gear drive of the present invention is less noisy than a conventional planetary gear system.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.